Abstract
The western honey bee, Apis mellifera, lives worldwide in approximately 102 million managed hives but also wild throughout much of its native and introduced range. Despite the global importance of A. mellifera as a crop pollinator, wild colonies have received comparatively little attention in the scientific literature and basic information regarding their density and abundance is scattered. Here, we review 40 studies that have quantified wild colony density directly (n = 33) or indirectly using genetic markers (n = 7) and analyse data from 41 locations worldwide to identify factors that influence wild colony density. We also compare the density of wild and managed colonies at a regional scale using data on managed colonies from the Food and Agriculture Organization (FAO). Wild colony densities varied from 0.1 to 24.2/km(2) and were significantly lower in Europe (average of 0.26/km(2)) than in Northern America (1.4/km(2)), Oceania (4.4/km(2)), Latin America (6.7/km(2)) and Africa (6.8/km(2)). Regional differences were not significant after controlling for both temperature and survey area, suggesting that cooler climates and larger survey areas may be responsible for the low densities reported in Europe. Managed colony densities were 2.2/km(2) in Asia, 1.2/km(2) in Europe, 0.2/km(2), in Northern America, 0.2/km(2) in Oceania, 0.5/km(2) in Latin America and 1/km(2) in Africa. Wild colony densities exceeded those of managed colonies in all regions except Europe and Asia. Overall, there were estimated to be between two and three times as many wild colonies as managed worldwide. More wild colony surveys, particularly in Asia and South America, are needed to assess the relative density of wild and managed colonies at smaller spatial scales.